Surgical cannulae are well known in the art. Such instruments are essentially tube-like elements which are inserted into surgical openings so that they line and maintain the openings. Surgical cannulae can be used for a wide variety of different purposes, and their particular construction tends to vary accordingly.
For example, some surgical cannulae are designed to serve as an irrigation passageway between the surgical site and the region outside the body. In this case, the cannulae, sometimes referred to as "irrigation cannulae", tend to be of relatively simple construction, and are frequently little more than a hollow tube, with or without an associated stopcock.
Other surgical cannulae are designed to serve as a protective liner for the surgical opening. These cannulae, sometimes referred to as "instrument cannulae", are used to minimize tissue trauma during the insertion, use and removal of surgical instruments to and from the surgical site. Since the surgical site is frequently well irrigated, particularly during arthroscopic surgery, these cannulae typically have some sort of fluid seal disposed across the cannula's central opening so as to prevent the disruptive backflow of fluid through the cannula.
Ideally, the fluid seal in an instrument cannula should be able to do three things well: first, it should be able to pass an instrument easily therethrough so that the instrument can reach the surgical site from a point outside the body; second, it should be able to establish an effective fluid seal about an instrument inserted into the cannula, and maintain it while the instrument is worked around the surgical site, so as to prevent the annoying backflow of fluid through the cannula; and third, it should be able to establish an effective fluid seal on its own across the cannula's central opening when no instrument is inserted into the cannula.
Unfortunately, fluid seals of the sort currently found in instrument cannulae have proven incapable of satisfying all three of these requirements. For example, at least one existing instrument cannula uses as its fluid seal a single flat resilient member which extends across the cannula's central opening. The flat resilient member has a slit at its center which permits an instrument to pass through the member to reach the surgical area. Unfortunately, however, this seal arrangement tends to leak badly, both when there is an instrument inserted in the cannula and when there is not.
An alternative seal arrangement is used in at least one other existing instrument cannula. This alternative seal arrangement comprises three flat parallel resilient members disposed across the cannula's central opening. Each resilient member has a single linear slit disposed therein which extends in a radial direction through the member's center point so as to allow an instrument access to the surgical site. These slits are oriented so that they extend at oblique angles relative to one another, in order to minimize the disruptive backflow of fluid through the cannula. While such a seal arrangement is somewhat better at eliminating fluid backflow than the aforementioned single flat seal arrangement, it still allows significant leakage to occur both when an instrument is inserted in the cannula and when one is not.